Many people realize that smartphones track their locations. But what if you actively turn off location services, haven’t used any apps, and haven’t even inserted a carrier SIM card?

Even if you take all of those precautions, phones running Android software gather data about your location and send it back to Google when they’re connected to the internet, a Quartz investigation has revealed.

Since the beginning of 2017, Android phones have been collecting the addresses of nearby cellular towers—even when location services are disabled—and sending that data back to Google. The result is that Google, the unit of Alphabet behind Android, has access to data about individuals’ locations and their movements that go far beyond a reasonable consumer expectation of privacy.

Quartz observed the data collection occur and contacted Google, which confirmed the practice.

The cell tower addresses have been included in information sent to the system Google uses to manage push notifications and messages on Android phones for the past 11 months, according to a Google spokesperson. They were never used or stored, the spokesperson said, and the company is now taking steps to end the practice after being contacted by Quartz. By the end of November, the company said, Android phones will no longer send cell-tower location data to Google, at least as part of this particular service, which consumers cannot disable.

“In January of this year, we began looking into using Cell ID codes as an additional signal to further improve the speed and performance of message delivery,” the Google spokesperson said in an email. “However, we never incorporated Cell ID into our network sync system, so that data was immediately discarded, and we updated it to no longer request Cell ID.”

It is not clear how cell-tower addresses, transmitted as a data string that identifies a specific cell tower, could have been used to improve message delivery. But the privacy implications of the covert location-sharing practice are plain. While information about a single cell tower can only offer an approximation of where a mobile device actually is, multiple towers can be used to triangulate its location to within about a quarter-mile radius, or to a more exact pinpoint in urban areas, where cell towers are closer together.

The practice is troubling for people who’d prefer they weren’t tracked, especially for those such as law-enforcement officials or victims of domestic abuse who turn off location services thinking they’re fully concealing their whereabouts. Although the data sent to Google is encrypted, it could potentially be sent to a third party if the phone had been compromised with spyware or other methods of hacking. Each phone has a unique ID number, with which the location data can be associated.

The revelation comes as Google and other internet companies are under fire from lawmakers and regulators, including for the extent to which they vacuum up data about users. Such personal data, ranging from users’ political views to their purchase histories to their locations, are foundational to the business successes of companies like Facebook and Alphabet, built on targeted advertising and personalization and together valued at over $1.2 trillion by investors.